MXPA06010511A

MXPA06010511A - Method and system for allocating time slots for a common control channel.

Info

Publication number: MXPA06010511A
Application number: MXPA06010511A
Authority: MX
Inventors: Vincent Roy; Paul Marinier
Original assignee: Interdigital Tech Corp
Priority date: 2004-03-16
Filing date: 2005-03-03
Publication date: 2007-01-17
Also published as: CA2559715A1; WO2005089133A3; US20050207373A1; BRPI0508162A; AU2005222812A1; KR20060131978A; WO2005089133A2; NO20064673L; EP1730971A2; IL178081A0; JP2007529954A; AU2005222812B2

Abstract

A method and system for allocating a time slot to each of the base stations for a communication channel to each of a plurality of base stations in a wireless communication system is disclosed. In a wireless communication system, a coverage area of the system is divided into a plurality of cells and each cell is served by a base station. The system receives a list of base stations which need to be configured along with a list of time slots available to transmit the communication channel. A time slot for the communication channel is allocated to each of the base stations in the list based on interference measured at each of the base stations in the list.

Description

When two cells belonging to the same subsystem use the same time interval to transmit a CCPCH, the reception of a WTRU of the CCPCH in a cell can be determined to a certain degree by the interference created by the transmission of the CCPCH by the other cell. The terminology "subsystem" refers to a set of TDD cells that can interfere with each other due to their relative proximity. If the level of this co-channel interference is too high, severe degradation of the operation of the WTRUs served by the cell can occur. Examples of impacts resulting from poor PCCPCH reception include delays in user access to a Radio Access Network (RA), service gaps, and degradation of key radio resource management functions such as transfers and control of power. Similarly, poor operation on the SCCPCH could result in unacceptable delays in call set-up times and reduced performance when the SCCPCH is used to transmit user data. To avoid this degradation, the system operator may decide to avoid having neighboring cells that use the same time intervals for their CCPCHs. If cell A and cell B are two neighboring cells, the time intervals used by a CCPCH in cell A would typically not be used in cell B, or could possibly be used for the transmission of dedicated channels (DCH) with certain limitations, as a limitation of the transmission power over that time interval. To ensure a minimum separation between the two cells using the same time interval for a CCPCH, a fixed reuse pattern (FRP) can be applied. In an FRP, the time intervals are assigned according to a regular pattern depending on the position of the base stations. An FRP technique can be used relatively easily as long as the base stations are deployed according to a geometrically regular pattern and the propagation conditions are relatively homogeneous throughout the deployment area. This can be considered to be the case in certain classic macrocell deployments, although not in all scenarios. Unfortunately, there are many situations where the conditions mentioned above are not met. For example, in microcellular and inland deployments, the irregularity of certain geographic features together with the problems of site acquisition will probably prevent the deployment of base stations according to regular frames. In these same environments, the propagation conditions are not necessarily homogeneous. In the case of a microcellular environment at street level, the propagation conditions between the two cells that are on the same street are radically different from the propagation conditions between two cells that are in streets perpendicular to each other. Furthermore, even in spite of the problems of site acquisition and uniform propagation conditions, the deployments of microcells and picocells that use a perfect geometric pattern may be undesirable from a capacity point of view since the. Traffic is highly non-uniform in those environments. In those situations, FRP techniques simply can not be used and the operator has to rely on trial and error to assign the appropriate time intervals to the CCPCH. If this trial and error process is carried out before the launch of the commercial service, this process would require extensive field measurements. Alternatively, if this trial and error process is carried out on a live network, it could result in poor quality perceived by the users until the appropriate parameters are found. In another alternative, the operator can use a radio frequency path loss prediction tool before the trial and error process, but that also requires extensive field measurements and calibrations. As a result, this process is costly and inefficient.

THE INVENTION A method and system for allocating a time slot to each of the base stations for a communication channel is described. In a wireless communication system, a coverage area of the system is divided into a plurality of cells and each cell is served by a base station. The system allocates time slots for a communication channel, such as a CCPCH, to each of the base stations in the list, based on the interference measured in each of the base stations in the list.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a wireless communication system according to the present invention. Figure 2 is a flow diagram of a process for automatically assigning a time slot to a cell for the communication channel according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED MODALITIES The present invention will be described with reference to the Figures of the drawings, where similar numbers represent similar elements therethrough. Hereinafter, the terminology "WTRU" includes but is not limited to a user equipment, a mobile station, a fixed or mobile subscriber unit, a pager, or any other type of device capable of operating in a wireless environment. When referenced here later, the terminology "base station" includes but is not limited to a Node B, a site controller, an access point to any other type of interconnection device in a wireless environment. Also, the term "CCPCH time slot" will be used to refer to any time slot that is used to transmit the CCPCH (either PCCPCH or SCCPCH). The present invention is a system and method that automatically and adaptively traces each base station in a wireless communication system to an appropriate CCPCH time slot. The method of the present invention can be implemented in a radio network controller (R C) as an advanced function of the Radio Resource Management (RRM) function, or in a program planning tool and autonomous programming systems. The present invention can be. implemented to assign radio resources to any of the PCCPCH or SCCPCH time slots. For simplicity, the present invention will be described primarily with reference to PCCPCH. However, it should be understood that the present invention could be used for the automatic configuration of any other CCPCH time slots, such as the SCCPCH time slots. The invention can also be broadly applied to other types of time slots in any other communication channels. Figure 1 shows a wireless communication system 100 according to the present invention. The system 100 comprises a plurality of base stations 104a-c and a radio network controller (RNC) 106. The coverage area of the system 100 is divided into a plurality of cells 108a-c and each cell 108a-c is served by a station separate base 104a-c, respectively. The base stations 104a-c transmit system parameters, via the PCCPCH, which are necessary to allow the WTRU, such as the TRU 102, to communicate with the base stations 104a-c. A list of the allowed time intervals that can be assigned to the CCPCH is provided to the RNC 106.. In assigning the time slots for the CCPCH, the RNC 106 has access to a list of base stations 104a-c. The RNC 106 is performed, in a sequential and iterative process, the allocation of the CPCCH time slot to the cell by each of the base stations 104a-c in the list of base stations 104a-c. The allocation of the interval to the cell is based on the interference measurements, so that the level of interference received at each base station 104a-c is minimized. Figure 2 is a flow diagram of a process 200 for assigning time slots in a wireless communication system according to the present invention. The example used here below will refer to a CCPCH. However, this is only by way of example and not limitation. It should be understood by those skilled in the art, that other types of channels may be implemented in the present invention. In the initial state, base stations within a subsystem are deployed and ready to be activated. None of the cells are assigned a PCCPCH time interval. In this state, all base stations of a subsystem are identified, and a list of base stations that need to be configured are provided as an entry along with a list of available time slots to transmit the CCPCH and a maximum number of iterations that the process 200 must perform (step 202). In the case of an initial download of the system, the list of base stations would consist of all the cells in the system. In other scenarios, the list of base stations could include new base stations that have been deployed in an existing radio network or could include a subset of cells in a system for which it is necessary to optimize the allocation of the CCPCH time slot to the cell. Preferably, the list of base stations is provided by the operator of the wireless system as an input before activating automatic allocation of the time slot to the cell. The process 200 then allocates a time slot to a CCPCH to each of the base stations in the list based on the interference measured in each of the base stations as will be explained in detail below. The preferred trace of the CCPCH time slots to the base stations is the only one that produces the lowest interference in the CCPCH time slots as perceived by each base station. The process 200 can be used to effect the total automatic configuration or a partial automatic configuration. The total automatic configuration is a process performed on all the base stations in the system, which infers that the list of base stations received as an entry in step 202 would include all the base stations of the system. Partial automatic configuration is a process performed when new additional cells are deployed in an existing system when the radio network expands and infers that the list of base stations received in step 202 would include only a subset of the base stations in the system. The process 200 can be used to perform the partial automatic configuration or the total automatic configuration to obtain a better performance on the PCCPCH. The process 200 is an iterative process. At the beginning of each iteration, it determines if any of the two exit conditions are satisfied (step 204 and 206). The first output condition is that the allocation of the time interval to the cell of the current interaction does not change from the assignment in the previous iteration (step 204). This condition can be satisfied only if the current iteration is not the first iteration that the process 200 is performing. If this first output condition is satisfied, the process ends, if not, the process 200 further determines that the second output condition is satisfied, (ie, if a maximum number of iterations has been made) (step 206). The maximum number of iterations is received as an entry in step 202. If the maximum number of iterations has been performed, process 200 ends. Otherwise, process 200 proceeds to step 208. A first base station is selected in the list of base stations (step 208) and the first base station is activated to measure and report the interference it perceives over each of the ranges of CCPCH time included in the list of available CCPCH time slots (step 210). It should be noted that base stations are not required to be classified in any particular order in the list of base stations. Nevertheless, the base stations could be classified according to their geographic coordinates, the date in which they have been deployed or any other criteria. The first base station is assigned the CPCCH interval for which the interference measurement was the lowest, and the base station begins transmission of the CCPCH over the selected time interval (step 212). In the case where multiple CCPCH ranges have the same interference measurements, the first time interval is selected in the list of assigned CCPCH time intervals. Then it is determined if there are some other base stations that remain in the list (step 214). If there are no other base stations remaining in the list, process 200 returns to step 204. If a remaining base station exists, process 200 selects the next base station in the list of base stations (step "216), and proceeds to step 210. Process 200 continues to implement steps 210-216 for all remaining base stations in the list in the same manner and allocates the appropriate PCCPCH time slots to each base station, allowing a wireless communication system to automatically configure its assigning PCCPCH ranges to base stations, the present invention frees the operator of the burden of previously planning and allocating radio resources to the PCCPCH including the comprehensive field measurements campaign and the use of a complex interference prediction tool when the system is deployed or increased, although the features and elements of the present invention were described in the Preferred alties in particular combinations, each feature or element can be used alone without other features and elements of the preferred embodiments or in various combinations with or without other features and elements of the present invention.

Claims

CLAIMS 1. In a wireless communication system where a coverage area of the system is divided by a plurality of cells, and each cell is served by a base station, a method for dynamically assigning a time interval to each of the base stations by a common physical control channel (CCPCH) comprising: (a) receiving as an entry a list of base stations that need to be configured together with a list of available time slots for transmitting the CCPCH; and (b) automatically assign a time slot for the CCPCH to each of the base stations in the list based on the interference measured in each of the base stations in the list. The method according to claim 1, wherein step (b) comprises: (c) selecting a base station from the list of base stations; (d) having the selected base station measure and report the perceived interference in each time slot available for the selected base station; (e) assigning a time interval with lower interference to the selected base station; and (f) repeating steps (c) - (e) for the remaining base stations in the list of base stations. 3. Method according to claim 1, wherein the CCPCH is a primary CCPCH. 4. The method according to claim 1, wherein the CCPCH is a secondary CCPCH. The method according to claim 1, wherein the base stations in the list of base stations are classified according to the geographical coordinates of the base station. The method of claim 1, wherein the base stations in the list of base stations are classified according to the deployment date of the base station. 7. Radio network controller (RNC) for assigning a time slot to a base station for a common physical control channel (CCPCH) in a wireless communication system, where a coverage area of the system is divided by a plurality of Cells and each cell is served by a base station, the RNC comprises: means for receiving as an input, a list of base stations which need to be configured together with a list of available time slots for transmitting the CCPCH; and means for assigning a time slot for a CCPCH to each of the base stations in the list, based on the interference measured in each of the base stations in the list. 8. RNC according to claim 7, wherein the allocation means comprises: means for selecting a base station from the list of base stations; means for selecting a time interval between the allowed time intervals for each base station; means for requesting that the base station measure and report the perceived interference in each time slot allowed by each base station; and means for assigning a time interval with the lowest interference to each base station. 9. RNC according to claim 7, wherein the CCPCH is a primary CCPCH. 10. RNC according to claim 7, wherein the CCPCH is a secondary CCPCH. 11. RNC. according to claim 7, wherein the base stations in the list of base stations are classified according to the geographical coordinates of the base station. 12. RNC according to claim 7, wherein the base stations in the list of base stations are classified according to the deployment date of the base station. 13. In a wireless communication system having a plurality of cells, each cell being served by a base station, a method for dynamically assigning a time slot to each of the base stations for a communication channel comprising (a) receive a list of base stations that need to be configured; (b) receive a list of available time slots to transmit the communication channel; and (c) automatically assigning the time interval for the communication channel to each of the base stations in the list based on an interference measured in each of the base stations in the list. The method of claim 13, wherein step (c) comprises: (d) selecting a base station from the list of base stations; (e) having the selected base station measure and report the perceived interference in each time slot available by the selected base station; (f) assigning a time interval with the lowest interference to the selected base station; and (g) repeating steps (d) - (f) for the remaining base stations in the list of base stations. The method according to claim 13, wherein the base stations in the list of base stations are classified according to the geographical coordinates of the base station. The method according to claim 13, wherein the base stations in the list of base stations are classified according to the deployment date of the base station.